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Starboard motor Slightly higher temps and fuel burn

R

rmm

Regular Contributor
"1988 454s FWC with 1200hrs -

"1988 454s FWC with 1200hrs - noticed my starboard motor seems to be running about 10-15 degrees hotter than port and is burning about 1-2GPH more. Also seems to steam and gurgle more than the other, is a wet exhaust. Impeller is new. Running temp is about 160-165. Took temps with heat gun on manifolds, risers and elbows on both motors.

Star manifold-148-155 or so
riser - 118-130
elbow - 128-150

Port manifold - 148-155
riser - 110
elbow - 108

Any thoughts? Anything to be concerned with?"
 
"You bet! Better make a hot r

"You bet! Better make a hot run up the river, then shut it right down and pull a few plugs. (Avoid any idling at all.) If they are stark white, as I suspect, the motor is running too lean. That means both more fuel burned and a hotter exhaust temperature.

Jeff"
 
"If it's too lean it can&#

"If it's too lean it can't be burning more fuel unless the RPMs are raised significantly. Seeing a gallon or two difference in the GPH reading between two motors isn't unusual (especially carb'ed engines) UNLESS is represents a sudden change.

With the elbow temp difference, I'd be looking for a restriction in the water passage in the elbows due to corroded cast iron flakes, especially if the temp creeps up with time at RPM."
 
"A couple of thoughts from me.

"A couple of thoughts from me. The last time I had an engine sustain a sudden 10% rise in consumption, it was caused by a bad spark plug wire. Still running smooth, but on 7 cylinders. This was quickly noted on the flowscans. An easy way to remember the lean/hot thing is that a RICH mixture sends unburned gas out the exhaust, which has an evaporative COOLING effect. I've spent many an hour in light planes, and getting the mixture correct using an EGT guage has made the difference in actually having enough fuel or not.
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"Plugs look normal. I should h

"Plugs look normal. I should have noted, I checked the risers/elbows on both sides of the starboard engine and got the same readings. The risers/elbows are 2 years old. Maybe I will try flushing the oil cooler and see what comes out.

Given the motor is still operating within "normal" ranges would think is OK. These motors do have 1200 hrs and would expect them to run slightly different. I know for example the port motor oil pressure gauge runs at 30-35 psi at 3000rpm and the strboard at 40-45 psi."
 
Boat in fresh or salt water?

Boat in fresh or salt water?

how do you shaft & rudder zincs appear after a season?

How often do you change your pencil zincs?
 
"Something else I see quite cu

"Something else I see quite curious. You measure a lower temp on the manifolds (exhaust?) than the engine temp. Normal thermostat engine exit temp is mid 160's, then it proceeds to cool the manifolds, increasing in temp. Manifold exit temp should be 180/190 degrees. You are measuring 10 deg LOWER than the engine temp?? Something wrong here."
 
"Chesapeake Bay, pencil zincs

"Chesapeake Bay, pencil zincs change at least one a season, what would the shaft and rudder zincs have to do with it?

I will check the temps again this weekend. The temps readings are measured with infrared heat gun on outside of exhaust manifolds. I would say they are close or same as dash gauge reading, dash readings may be slightly higher, hard to tell way gauge is designed. I did scan the entire top side of motors and hoses and temp readings seemed to be uniform with no odd spikes."
 
"If your exh. manifolds are re

"If your exh. manifolds are really 140's to 150's at cruise, you have likely a 140 degree thermostat, or defective/missing thermostat."
 
"once a season really isn'

"once a season really isn't often enough if you're south of the elk river or use the boat most of the season.

The condition of the other zincs will provide an indiction of the galvanic activity the boat is exposed to. If they are eroded after a season, the pencil zincs would have been spent long before.

When you scan the manifolds, try to stay on the upper half, where the water jacket is. Also, keep the gun fairly close to the cast iron unless you know you have a really small spot size."
 
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